This invention relates to a direction-selectable sending-out pump, in more detail to a direction-selectable sending-out pump capable of supplying liquid selectably to two routes from one tank, which may find use, for example, in supplying washer liquid selectably to the front and rear windows of a car.
In general, such a car as supplies washer liquid to its front and rear windows is provided with two sets of washer-liquid tanks and sending-out pumps, each being for each window. Such separate provision of washing devices, however, gives rise to disadvantages such as space occupation an cost rise.
To solve the above problems, a system has been devised in which one direction-selectable sending-out pump sends out washer liquid from one common washer-liquid tank selectably to two washing routes.
FIG. 14 shows an axial-direction sectional view of the above-mentioned conventional direction-selectable sending-out pump, and FIG. 15 shows a XV--XV sectional view for FIG. 14 (Patent laying open No. 60-6096).
In the pump 10 shown, a centrifugal impeller 14 is fixed on the output shaft of a reversible motor, and on the side of a housing 16 accommodating the impeller 14 there are manifold chambers 20 and 22 partitioned vertically by an elastic membrane 18. The upper and lower manifold chambers 20 and 22 are connected to the housing 16, respectively, by tangent-direction conduits 24 and 26 symmetrically positioned with respect to the housing 16. In the manifold chambers 20 and 22, outlet apertures 28 and 30 are opened at positions facing the elastic membrane 18 and the edges of these outlet apertures 28 and 30 are formed into valve seats.
With this structure, when the impeller 14 rotates counter-clockwise in FIG. 15, the liquid flowing through the axial-direction hole 32 into the housing 16 flows through both the tangent-direction conduits 24 and 26 into the manifold chambers 20 and 22, respectively. In this process, the pressure in the tangent-direction conduit 24 along the rotational direction of the impeller 14 becomes higher than that in the tangent-direction conduit 26 against the rotational direction of the impeller 14. The pressure difference thus raised will bring the elastic membrane 18 into tight contact with the valve seat so as to close the outlet aperture 30 and open the outlet aperture 28, with liquid being sent out through the outlet aperture 28.
On the other hand, when the impeller 14 is rotated clockwise, the outlet aperture 28 will be closed by the elastic membrane 18 and the outlet aperture 30 opened, with liquid being sent out through the outlet aperture 30.
In such a process, liquid is allowed to be sent out selectably into two flow paths.
However, the above-described direction-selectable sending-out pump 10 has problems as follows.
Both the tangent-direction conduits 24 and 26 are located on the outlet side with respect to the inlet side (the axial-direction hole 32) of the pump, though with different angles. Because on this positioning, rotation of the impeller 14 makes the pressures within both the tangent-direction conduits 24 and 26 higher than that in the inlet side irrespective of rotational directions, and on the other hand, rotation of the impeller 14 produces pressure difference between both the tangent-direction conduits 24 and 26 depending on the rotational direction of the impeller. The working mechanism for bringing the elastic membrane 18 into contact with the valve seat is based merely on utilization of this pressure difference.
Both the tangent-direction conduits 24 and 26 simultaneously become positive in pressure as described above. Therefore, if presence of contaminants, etc. has caused imperfect sealing of the valve seat normally to be sealed by the elastic membrane 18, a trouble is caused that liquid is sent out, though with low pressure, into the outlet side normally to be shut out. The same leak trouble occurs also at the rise period of pump, when the power supply voltage is lowered, when the flow-path resistance between pump and outlet nozzle, and so on, where the pressure difference is not large enough to bring the elastic membrane into perfect contact with the valve seat.